Fully integrate TinyASM functionality into Firedrake

[JDBetteridge]

Describe the current issue
As a result of incorporating TinyASM, Firedrake is carrying around two C++ files and as a result now requires a pybind11 dependency. The content of these files could probably be written in C or Cython and moved into Firedrake, TinyASM doesn't need to be a separate package.

Describe the solution you'd like
Rewriting TinyASM in C/Cython and integrating it into the build system without relying on pybind11.

Describe alternatives you've considered
Dropping support for TinyASM.

Additional info
N/A